1. Field of the Invention
The present invention relates to a switching device using tunnel injection, which are particularly adapted for wide bandgap semiconductor device and a method for manufacturing the switching device. The invention particularly relates to a heterojunction device using an insulated gate structure.
2. Description of the Related Art
The bandgap of SiC is wide, and it's maximum breakdown field is larger than silicon (Si) one figure. Furthermore, the natural oxide of SiC is silicon oxide (SiO2), and the thermal oxidation film can be formed easily on the surface of SiC by a method the same as that for Si. For this reason, SiC is anticipated for use in a high-speed/high breakdown voltage switching device used in a battery car, and in-particular when it is used as a high power unipolar/bipolar device, it is hoped that SiC will provide a superior material. For example, Japanese Patent Laid-Open-no. 10-233503 discloses earlier SiC power MOSFET. In this earlier SiC power MOSFET, an n− type SiC epitaxial layer is formed on a heavily doped n+ type SiC substrate. And, in a predetermined region in a top surface of the epitaxial layer, p− type body regions and n+ type source regions are formed. In addition, through a gate insulation film, a gate electrode is disposed above the n− type SiC epitaxial layer, and the gate electrode is covered by an inter-layer insulation film. Source electrodes are formed so as to contact with p− type body regions and n+ type source regions and, a drain electrode is formed on the back surface of the n+ type SiC substrate.
In a bias condition such that the voltage is applied between the drain and source electrodes, when a positive voltage is applied to the gate electrode, a channel region of an inversion type is formed on the top surface of the p− type body region facing the gate electrode, and current conducts from the drain to source electrodes. By removing the voltage applied to the gate electrode, the drain electrode is electrically isolated from the source electrode, and a switching function is manifested.